The Core Mass Spectrometry Facility (CMSF) is being proposed as a new Cancer Center shared resource. The CMSF is the successor to a prior UCSF mass spectrometry facility with which the Cancer Center cooperated for the past three years. The success of the cooperation and the increased need of members for mass spectrometry services has lead the Cancer Center to assume management of this facility. Effective provision of mass spectrometry services requires highly skilled personnel to provide effective guidance for non-expert investigators, and a substantial instrumentation base. The senior staff of the CMSF consists of a faculty director, a Ph.D. manager, and two faculty co-directors of operations, who also are P.l.s and/or investigators on competitively-funded research projects that develop and apply novel mass spectrometry techniques. These projects share use and support of the instrumentation, and assist with provision of funds for acquisition of advanced technology. This organizational structure assures timely availability of advanced mass spectrometry capability to Cancer Center members. The CMSF also benefits from cooperation with the substantial mass spectrometry efforts distributed'across the campus and at neighboring institutions, including nationally-prominent facilities and projects. The CMSF operates and maintains four mass spectrometers, four HPLC systems, two sample preparation robots at its main location, and has access to two additional mass spectrometers and an HPLC instrument at a satellite site. This instrumentation, along with an array of associated bioinformatics hardware and software enables the facility to offer a comprehensive suite of proteomic MS services to Cancer Center members. Representative services include multiple approaches to protein identification, quantitation, molecular mass determination, and data interpretation. In addition, consultation with regard to experimental design, sample preparation, data publication and grant writing are provided. The CMSF has a strong commitment to educating its users. Several different venues enable this process including seminars, training classes, and electronic mailings, which keep users abreast of the latest developments in sample preparation, MS technology, instrumental design and labeling chemistries as well as basic MS principles.